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A recurrence relation for elliptic divisibility sequences

Number Theory 2024-03-19 v2

Abstract

In literature, there are two different definitions of elliptic divisibility sequences. The first one says that a sequence of integers {hn}n0\{h_n\}_{n\geq 0} is an elliptic divisibility sequence if it verifies the recurrence relation hm+nhmnhr2=hm+rhmrhn2hn+rhnrhm2h_{m+n}h_{m-n}h_{r}^2=h_{m+r}h_{m-r}h_{n}^2-h_{n+r}h_{n-r}h_{m}^2 for every natural number mnrm\geq n\geq r. The second definition says that a sequence of integers {βn}n0\{\beta_n\}_{n\geq 0} is an elliptic divisibility sequence if it is the sequence of the square roots (chosen with an appropriate sign) of the denominators of the abscissas of the iterates of a point on a rational elliptic curve. It is well-known that the two sequences are not equivalent. Hence, given a sequence of the denominators {βn}n0\{\beta_n\}_{n\geq 0}, in general does not hold βm+nβmnβr2=βm+rβmrβn2βn+rβnrβm2\beta_{m+n}\beta_{m-n}\beta_{r}^2=\beta_{m+r}\beta_{m-r}\beta_{n}^2-\beta_{n+r}\beta_{n-r}\beta_{m}^2 for mnrm\geq n\geq r. We will prove that the recurrence relation above holds for {βn}n0\{\beta_n\}_{n\geq 0} under some conditions on the indexes mm, nn, and rr.

Keywords

Cite

@article{arxiv.2102.07573,
  title  = {A recurrence relation for elliptic divisibility sequences},
  author = {Matteo Verzobio},
  journal= {arXiv preprint arXiv:2102.07573},
  year   = {2024}
}

Comments

Final version of the paper

R2 v1 2026-06-23T23:10:20.255Z